1. Field of the Invention
The present invention relates to a laser light receiving apparatus, and particularly to such an apparatus which facilitates accurate reception of a desired laser light without being affected by ambient noise light.
2. Related Art Statement
The laser light receiving apparatus is used conventionally for the familiar door-sensor, but also for a counter or a sensor of bodies passing-through a certain area, a distance sensor, a speed sensor of moving bodies and the like. An outlined arrangement thereof is shown in FIG. 8.
The conventional laser light receiving apparatus as shown in FIG. 8 is composed of a light receiving section 1 having a photo-electric converter which consists of a photo-diode or the like for converting a received laser light into an electric pulse signal, a signal amplifying section 2 for amplifying the pulse signal derived from the light receiving section 1 to a predetermined level, a signal detecting section 3 for detecting the amplified pulse signal derived from the signal amplifying section 2 and an informing section 4 formed, for instance, of a loud speaker, which is driven by the signal detection section 3.
When the laser light receiving apparatus is used as a door sensor, a counter for bodies passing-through a given area and the like, an establishing circumstance is substantially the same, in which a received light signal is regular and stable, so that any light disturbance caused by noise light is not specially considered in the conventional condition.
Consequently, when the above mentioned conventional apparatus is used outdoors and further mounted on a moving body, the apparatus receives various noise lights and erroneous operation results. For example, when the day light is instantly blocked by an obstacle, that is, a street lamp, a guard rail, a suspension bridge or the like, a noise light pulse is caused by the variation of the input light in the conventional apparatus.